The MV bulb can be as close as 6" from the tops, MV is the coolest running of the HID family, but still if you touch it while running it will burn you. I have gotten overspray from foliar feeding on the bulb before and it didn't blow up or anything like a HPS would. I posted some more info about these lights here:
http://boards.cannabis.com/showthread.php?t=7419
I like the color corrected bulb, also called soft white for flowering, the spectrum is better, as it does produce useable light for photosynthesis, just not as much as other HID does, but the UV-B triggers the plant to produce THC as a defence to the UV radiation, or at least that is what I understand from my reading.
L0rdsOth :D